As a alternative, you could also look into the Freescale Symphony Soundbite: basically a Motorola 563xx based DSP board with onboard AKM codecs and everything. It's not lightning fast at 180 MIPS, but should be enough for iir crossover work and at $150 quite a nice package.

However, I'm not quite sure if I'll be venturing down that path, looks like it is necessary to do quite some configuration and programming with those beyond just plugging in the parameters.. My experience with DSP's and more advanced digital electronics is limited to say the least, and although I could probably dive in to it, I need something I can get to work with a modest effort, lest I'll never complete my project!

Double precission is always an option, and going floating point will have a significantly higher price tag. TI has some evaluation/development boards for the 67xx floating point dsp's but these are imho too expensive for crossover development.

But even an 150-ish MIPS legacy Motorola will be able to do quite complex crossover work. As long as you stay away from long FIR filters, dozens of biquads on decent (96k) samplerates with double precision shouldn't be a problem.

As far of ease of programming, there is a certain learning curve involved. Most eval-boards will ship with decent tutorials an most often a dsp-library, often featuring standard processing elements like FIRs, IIRs and FFTs.

The Red Rocks miniPROC is a good bet then. Reasonable cost, system level programming and from what I've seen, it does it with pretty good dynamic range. Based on TI TAS3103 audio processor it has all the blocks for an XO.http://focus.ti.com/lit/ds/symlink/tas3103.pdf

PC programmable with analog I/O. Nice, depending on exactly what you intend to do. But depending on what you do want to do, adding another 2 channels of audio output to your PC and some software might be all that is required.